1. Field of the Invention
This invention generally relates to electrical contacts and more specifically to a stacked printed circuit board connection system for making connections to printed conductors on single and multi-layered or stacked printed circuit boards used in high speed digital applications.
2. Description of the Prior Art
Typically, pins are mounted on printed circuit boards for interconnecting conductors on printed circuit boards with offboard circuits or components, such as by wire wrapping of conductors onto the pins. In some cases, such pins are used as test points. In other cases they provide electrical contact between printed circuits on stacked boards at different levels.
Numerous contact and interconnect arrangements have been proposed for mounting pins on printed circuit boards and for using conductive pins to interconnect printed conductors of stacked printed circuit boards or systems of modules of spaced printed circuit boards.
The objectives in the design of such contact arrangements include low assembly costs, good electrical contact (least resistance or maximum conductance) and ease and convenience of use.
In U.S. Pat. No. 2,283,040, pins are inserted into leaf springs of an electric plug device normally used in sockets. Spring receptacles, which expand upon the insertion of a pin, are also shown in U.S. Pat. Nos. 2,814,024 and 3,097,032. However, the considerations in designing electrical power receptacles or exteriorly-mounted sockets are significantly different than those for designing contacts to be received within plated through holes of stacked printed circuit boards. For one, the printed circuit board contacts of the type described herein are substantially smaller, are used in high density environments and frequently operate at much higher frequencies. Impedance matching, therefore, may become an important consideration in the printed circuit context while, of course, such is not a consideration in A.C. power circuits.
In U.S. Pat. No. 3,193,788, a connecting pin is disclosed which includes a plurality of resilient projections which abut against the internal surface of a cylindrical hole provided with conductive linings within the aligned holes or apertures in a multiple layered printed circuit board module. In U.S. Pat. No. 3,212,049, inwardly directed contacts form a tapered receptacle which makes contact with a pin. However, the tapered contacts do not significantly change their configuration upon insertion or removal of a pin, and do not change the degree of contact between the receptacle and the inner conductive surface of the individual printed circuit holes. The same is true of the socket assembly described in U.S. Pat. No. 3,218,606.
In U.S. Pat. No. 3,400,358, multiple bow contacts are uniformly spaced from each other, each of the bows having substantially the same external dimensions to form an elongate single plug that can pass through a series of aligned holes in different printed circuit boards. No pins are used to expand the plug. Each bow is arranged to make contact with another printed circuit board contact.
A board-to-board interconnect device is disclosed in U.S. Pat. No. 4,859,188 which uses slotted discs 24 to make contact with a wire 30 bridging the boards.
However, the prior art contacts tend to be bulky and are not suitable for use with high speed digital printed circuit boards which have holes, the interior surfaces of which are plated with thin layer conductors to which positive electrical contact must be made to maintain desired impedance levels and minimize losses. Also, the prior contacts do not offer the required performance packaging advantages for use on memory boards, computer hardware equipment and similar requirements where effective and economical use of available printed circuit board space is needed.
In U.S. Pat. No. 3,792,412 a printed wiring board terminal assembly is shown in which a square pin cooperates with an adapter sleeve which defines a plurality of longitudinal contacting nodes. Insertion of the pin causes the contacting nodes to expand radially to make electrical contact with the plated surface of a hole in a printed circuit board. However, because the contacting nodes are longitudinal, wiping action of the hole plated surface is incomplete and, therefore, conductivity may be impaired.